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the oygen-binding pigment in vertebrate RBCs
How does Hb affect the carrying capacity of blood?
the presence of Hb increase the O2 carring capacity by 60X over that of plasma
How do invertebrates transport O2 ?
Many have functionally similar oxygen binding proteins (chlorocruorin, hemerythrin, hemocyananin), but many including most insects have none
What is different about oxygen transport in anartic ice fish (Chaenichthids)?
they have no Hb because they live in very cold (hi PO2) water
What is the structure of Hemoglobin?
Hb is a protein with four polypeptide subunits, each with a heme (iron containing group which can reversibly bind a molecule of oxygen. Hb consists of two alpha and two beta subunits (in adults).
What drives the diffusion of oxygen into the blood?
- A pressure gradient.
- Oxygen is picked up where its partial pressure is high and is released where the partial pressure is lower.
- As oxygen diffuses into the blood, it binds to hemoglobin, increasing the PO2 gradient and driving diffusion of oxygen into red blood cells.
What does the ability of hemoglobin to bind and release oxygen depend on? (3 things)
- its affinity for oxygen
- the PO2 of its environment
- regulators (pH and 2,3 BPG) in the blood
When will Hb be fully saturated?
When PO2 of blood plasma is high, as in lung capillaries, each hemoglobin complex will carry four molecules of oxygen
Hb-O2 saturation curve
Shows the relationship between saturation of the hemoglobin polypeptides and PO2. The values follow a sigmoid curve
Positive cooperativity in Hb
- binding the first molecule of oxygen makes the second binding easier, and so on
- However, it takes a relatively greater PO2 to bind the fourth molecule and achieve 100 percent saturation
On average how much of the oxygen held by Hb is released as it circulates through the body, and why?
On average only 1/4 of the oxygen is released, the other 75% is kept as reserve for peak demands.
When is the reserve oxygen held by Hb used?
If a tissure is starved for O2 and its local PO2 falls below 40 mm Hg, the hemoglobin will release the reserved O2 to the starved tissue
- th PO2 where Hb is half saturated
- provides a measure of the affinity of the Hb for Oxygen
- Mb is the oxygen binding pigment in muscle
- It has a higher affinity (lower P50) for oxygen than Hb
What is the structure of Mb?
consists of one peptide and a heme, that can only bind one molecule of oxygen
What is the purpose of Mb?
It has a higher affinity for oxygen than hemoglobin and provides an oxygen reserve for high metabolic demands or for when blood flow is interrupted
Why do diving mammals have high concentrations of myoglobin in their muscles?
It helps them to stay under water for long periods
Muscles used for what have the most Mb?
muscles called on for extended periods of work frequently have more myoglobin than muscles used for short, intermittent periods
What is the affect of Carbon monoxide on the body?
- CO binds to hemoglobin with a much higher affinity than does oxygen, thereby inhibiting oxygen binding
- CO is a deadly poison, as it destroys the ability of hemoglobin to transport oxygen
How have Hbs affinities for oxygen evolved to suit different animals and why?
- The affinities of Hbs for O2 have evolve to fit the PO2 of the environment of the animal
- the Hb must have a high enough affinity to maximally load O2 at the respiratory surface (100% saturation), but if the P50 is foo low the Hb cannot properly unload the oxygen to the tissue resulting in a low PO2 in the tissues even at rest
Are the affinities of Hbs of animals from lo PO2 environments (hi altitude, lo PO2, water, etc.) hi or lo and why? What affect does this have on the PO2 of the tissues, how is this compensated for?
- The affinities of Hbs are hi to maximize loading. This means the tissue PO2 may be lo also
- however, affinity can be decreased in the tissues to facilitate unloading
How does human fetal Hb differ from adult Hb and why?
- fetal Hb has two y-globin chains instead of ß-globin, which results in a greater affinity for oxygen
- the difference in oxygen affinity facilitates transfer of oxygen from the mother's blood to fetal blood in the placenta
- Fetal Hb is less affected by BPG than adult Hb
- the influence of pH on the function (affinity) of hemoglobin
- Hi H+ concentration (lo pH) and 2,3 Biphosphoglyceric acid decreases Hb-O2 affinity
- the effect effect occurs when the pH of the blood falls and the H+ ions bind to the hemoglobin and decrease its affinity for oxygen
- the oxygen-binding curve shifts to the right
How does 2,3 BPG function as a regulator of hemoglobin?
- In RBCs BPG combines with deoxygenated hemoglobin and causes it to have a lower affinity for oxygen (shifts saturation curve to the right)
- the result is that the hemoglobin releases more of its bound oxygen to tissues than usual
When does BPG increase in a human, and how does the body respond?
- If a person goes to a high altitude or starts exercising BPG goes up
- in response hemoglobin releases more oxygen where it is needed
How is CO2 transported into the blood, and what happens to it once it is there?
- CO2 is highly soluble, moving easily through cell membranes into the blood, where the partial pressure of CO2 is lower
- most CO2 is transported as bicarbonate ion
- capillary endothelial cells and red blood cells produce carbonic anhydrase, which speeds conversion of CO2 to H2CO3
- the H2CO3 dissociates and bicarbonate ions enter the plasma in exchange for chloride ions (Cl- shift)
- this conversion reduces the partial pressure of CO2 promoting the diffusion of CO2 out of the tissue cells
How is CO2 released in the lungs?
- In the lungs, the CO2 and bicarbonate reactions are reversed, also catalyzed by carbonic anhydrase
- CO2 diffuses from blood plasma into the aveolar air and is exhaled
- as the PCO2 in the blood falls, more bicarbonate is converted into carbon dioxide
Which system regulates breathing?
breathing is controlled by the autonomic nervous system
How does the autonomic nervous system control breathing?
- the brain stem (medulla) generates and controls the breathing rhythm
- groups of pacemaker neurons within the medulla increase their firing rate just prior to inhalation
- these input to motor neurons to the diaphram, initiating inhalation
- when the firing stops, the diaphragm relaxes, and exhalation occurs
- normal exhalation is actually a passive elastic recoil of lung tissue, but it can be active
How does the body regulate breathing?
- When breathing demands are high, as during exercise, the motor neurons for the intercostal muscles are fired to increase inhalation and exhalation volumes
- brain areas above the medulla modify breathing to allow speech, eating, coughing, and emotional states
what provides the main feedback information for breathing rate?
PCO2, in mammals carbon dioxide is very high, but oxygen sensitivity is remarkably low
Where are carbon dioxide and/H+ sensors located?
they are located on the ventral surface of the medulla near the neurons that generate the breathing rhythm
Where are oxygen sensors locacated and what do they do?
- They are in tissue nodes on the aorta and carotid arteries called carotid and aortic bodies
- if PO2 of blood drops, chemoreceptors in these bodies send nerve impulses to the brain and breathing center
What are baroreceptors and where are they located?
- they monitor blood pressure
- they are located on the aortic and carotid arteries